Elimination of airborne chemical and biological warfare agents

ABSTRACT

The invention is directed to an apparatus made of atmospheric-pressure microwave plasma torches for elimination of toxic airborne chemical and biological warfare agents. The apparatus can purify the interior air of large volume in an isolated space such as buildings, public transportation systems, and military vehicles contaminated with chemical and biological warfare agents. The apparatus consists of several microwave plasma torches connected in series for elimination and burnout of toxic airborne warfare agents. Microwave radiation generates an atmospheric plasma torch in certain conditions. Oxidation mechanism in the torch flames eliminates the chemical and biological warfare agents.

FIELD OF THE INVENTION

The present invention relates generally to pollutant abatement and, inparticular, to an apparatus and process for eliminating and burning outpollutants in the interior air of large volume in an isolated space suchas buildings, public transportation systems, and military vehiclescontaminated by chemical and biological warfare agents. The chemical andbiological warfare contaminants are eliminated by their exposure to theflames of the microwave plasma torches.

BACKGROUND OF THE INVENTION

Protection of people against chemical and biological warfare agents isvery important and is very necessary in the present world environment.The threat of chemical and biological warfare agents increases in adomestic terrorist attack and in worldwide military conflict. Year 2001anthrax problems throughout the USA after 9-11 terror attack, 1995 sarinnerve gas attack on a Tokyo subway station, and the threat of toxicagents in 1991 Gulf War are a few examples of the worldwide threat ofchemical and biological warfare agents. There are several categories ofchemical warfare agents. They are (1) Nerve Warfare Agents, (a) Tabun,GA: CH₃)₂N—P(═O)(—CN)(—OC₂H₅, (b) Sarin, GB: CH₃—P(═O)(—F) (—OCH(CH₃)₂,(c) Soman, GD: CH₃—P(═O)(—F)(—CH(CH₃)C(CH₃)₃, (d) Cyclohexylmethylphosphonofluoridate, GF: CH₃—P(═O)(—F)(cyklo—C₆H₁₁), (e)Methylphosphonothioic acid S-(2-(bis(1-methylethyl)amino)ethyl) O-ethylester, VX: CH₃—P(═O)(—SCH₂CH₂N[CH(CH₃)₂]₂) (—OC₂H₅), (f) GE:Phosphonofluoridic acid, ethyl-, isopropyl ester, (g) VE:Phosphonothioic acid, ethyl-, S-(2-(diethylamino)ethyl) O-ethyl ester,(h) VG: Amiton, and (i) VM: Phosphonothioic acid, methyl-,S-(2-(diethylamino)ethyl) O-ethyl ester, (2) Blister and VesicantWarfare Agents, (a) Lewisite (L), (b) Mustard-Lewisite (HL), (c)Nitrogen Mustards (HN-1, HN-2, HN-3), (d) Phosgene Oxime (CX), and (e)Sulfur Mustards (H, HD, HT), (3) Blood Warfare Agents, (a) CyanogenChloride (CK), and (b) Hydrogen Cyanide (AC), and (4) Pulmonary WarfareAgents, (a) Chlorine, (b) Chloropicrin (PS), (c) Diphosgene (DP), (d)Phosgene (CG). There are also several biological warfare agents such asAnthrax, Botulinum Toxins, Brucellosis, Cholera, Clostridium PerfringensToxins, Congo-Crimean Hemorrhagic Fever, Ebola Haemorrhagic Fever,Melioidosis, Plague, Q Fever, Ricin, Rift Valley Fever, Saxitoxin,Smallpox, Staphylococcal Enterotoxin B, Trichothecene Mycotoxin,Tularemia, Venezuelan Equine Encephalitis. There may be other chemicaland biological warfare agents not listed above. But, those warfareagents must be also eliminated by the present invention.

The purpose of the present invention is a rapid and effectiveelimination of toxic substances in the interior air in an isolated spacesuch as buildings, public transportation systems, and military vehicles.The buildings, where the interior air must be purified, can be thepersonal dwellings, apartment buildings, office buildings, schoolbuildings, government buildings, and the commercial buildings. Thepublic transportation system includes automobiles, cars, buses, trains,ships, commercial airline airplanes, and the subway railroad system. Themilitary vehicles mentioned are military trucks, armored personnelcarriers, military buses, tanks, military ships, airplane carries,helicopters, and military airplanes. The toxic warfare agents mentionedabove have been traditionally incinerated by burn scrubbers. Theseburners tend to be large, inefficient, and expensive. On the other hand,the microwave plasma torch operated at the atmospheric pressure iscompact enough to be installed in a narrow space and is effective toeliminate the toxic agents diluted in a large flow rate of air.

Pollution control with respect to contaminated air as a carrier gas wasproposed in U.S. Pat. No. 5,468,356 issued to Uhm, one of the presentinventors, on Nov. 21, 1995. In that invention, contaminated air isexposed to microwave-generated plasma for oxidation by atomic oxygenwithout bulk heating within a simple cylindrical waveguide cavity at theroom temperature. Further, such plasma is generated within the cavity byintroduction of high-power microwave radiation passing through a weakelectric field to achieve air purification despite low electron energy.Pollution control with respect to contaminated air as a hot carrier gaswas proposed in U.S. Pat. No. 5,830,328 issued to Uhm, one of thepresent inventors, on Nov. 3, 1998. The plasma generated in a hot gaslike discharge gas from a combustion engine or like the discharge gasfrom an incinerator may oxidize the contaminants, purifying thedischarge air. The present invention is a combination of the above twoinventions, making use of an intense electric field in the microwaveradiations and use of the hot air in the torch flames of the presentinvention.

It is therefore an important object of the present invention to enhancethe electric field strength of the microwave radiation in order toachieve elimination of toxic warfare agents in a carrier gas by exposureto a plasma torch generated by concentration of the microwave on a smallspot.

Other object of the present invention is to simultaneously provide anelimination and burnout system that is effective against a wide range ofchemical and biological warfare agents with several plasma torchesconnected in series.

Another object is to overcome difficulties heretofore experienced inachieving efficient and rapid elimination of the toxic agents byoxidation with several plasma torches connected in series.

Additional objects, advantages and novel features of the invention willbe explained in part in the following description, and will be apparentto those skilled in the following experiment.

SUMMARY OF THE INVENTION

The present invention is the apparatus for simultaneous elimination andburnout of chemical and biological warfare agents diluted in air withseveral microwave plasma torches connected in series. Particularly, theapparatus is useful for purifying the interior air of large volume in anisolated space such as buildings, commercial transportation systems, andmilitary vehicles contaminated with chemical and biological warfareagents. High electric field strength and high-energy electrons providedby the plasma torch are needed to eliminate and bum out chemical andbiological warfare agents. The microwave plasma torches are connected inseries so that the contaminant air stream to be purified passessequentially from one plasma torch to the next, thereby increasing therequired residence time for optimum effect. The high temperature flamesof microwave plasma torches create a unique environment for efficientchemical reactions. Prolonging this unique environmental condition bysequential connection of optimum number of microwave plasma torches iscritically important for rapid purification of a large volume ofcontaminated air, creating a synergic effect caused by multiple plasmatorches. The number of the plasma torches is empirically determined.

The present invention is made of the magnetrons used in home microwaveovens. These magnetrons are inexpensive, commercially available andcompact. They are operated at a frequency of 2.45 GHz and their power isin the range of 0.6˜1.4 kW. The microwave intensity with a frequency of2.45 GHz from a magnetron is highest at the discharge tube. Theseintense microwaves at the discharge tube induce an intense electricfield, initiating electrical breakdown in the carrier gas containingchemical and biological warfare agents. The plasma torch generated bythe electrical breakdown due to the microwave electric field eliminatesand burns out chemical and biological warfare agents by oxidation, bymolecular breakdown, and by hot gases. The atmospheric plasma abatementsystem, which is simple and cost-effective, is the most suitable forpurification of air contaminants. The elimination experiment of anychemical warfare agent is almost impossible in an ordinary laboratorydue to safety issues. In this context, the experimentaliststraditionally carry out a simulated experiment by making use of toluenegas. Elimination efficiency of toluene as one simulated agent wasexperimentally measured by a gas chromatography system. For same reason,the biological warfare agents are not used in an ordinary laboratory.Therefore, the vitrification and burnout of dried and pulverized sewagesludge powder as the biological simulated agent were carried out.

BRIEF DESCRIPTION OF DRAWING FIGURES

A more complete appreciation of the invention and many of its attendantadvantages will be aided by reference to the following detaileddescription in connection with the accompanying drawings:

FIG. 1 is a block diagram illustrating the airborne warfare agentelimination system of the present invention;

FIG. 2 is a cross-sectional view of the three microwave plasma torchesconnected in series;

FIG. 3 is the transmittance of the toluene gas measured by the GasChromatography (GC) before and after the microwave discharges.

DETAILED DESCRIPTION

The present invention is the apparatus and scheme for a simultaneouselimination and burnout of chemical and biological warfare agentsdiluted in air with several microwave plasma torches connected inseries. The principles and operation of modular microwave plasma torchesof the present invention are described according to the drawings.

Referring now to the drawing in details, FIG. 1 diagrams the basicportion 10 of the present invention wherein air stream contaminated withchemical and biological warfare agents as input gas 16 enters thedischarge tube 12 made of an insulating dielectric material such asquartz or ceramics. According to the experimental results with variousquartz size, it was found that the most suitable plasma generationaccomplished when the inner diameter of the quartz tube with thickness1.5 mm is in the range of 22˜27 mm for the microwave frequency of 2.45GHz. Diameter of a typical plasma-torch flame is about 20 mm. The flamesize does not increase even if the internal diameter of the quartz tubeincreases.

The power supply 24, consisted of full-wave voltage double circuit,provides the electrical power to the magnetron 22 which generates themicrowave radiation and which is cooled by a cooling system 26, whichmust be capable of delivering at least 1000 liters per minute (1/min)cooling air. The magnetron 22 must be sufficiently cooled, because themagnetron efficiency is very sensitive to the temperature. The generatedmicrowave radiation from the magnetron 22 is guided through thewaveguide 18-c, passes through the three-stub tuning device 20, andenters the discharge tube 12 through the waveguide 18-b. The magnetron22 in the present invention is the low-power 2.45 GHz microwave sourceused in a typical home microwave oven. Some of the microwave radiationin the discharge tube 12 goes forward to the end of the waveguide 18-aand is reflected back to the discharge tube 12. The electric fieldinduced by the microwave radiation in the discharge tube 12 can bemaximized by adjusting the three-stub tuning device 20. The ignitiondevice 14 with its terminal electrodes inside the discharge tube 12 isfired to initiate plasma generation inside the discharge tube 12. Theplasma torch in discharge tube 12 is ignited by the combined action ofthe ignition device 14 and the electrical power provided by themicrowave radiation.

The torch flame in the discharge tube 12 is stabilized by the swirl gasinput 30. The swirl gas enters the discharge tube sideways creating avortex inside the discharge tube, stabilizing the torch flame andprotecting the discharge tube wall, made of quartz tube, from heatemitted by the flame of temperature with 5,000 degrees Celsius. Theswirl gas 30 plays important roles in the thermal insulation of thedischarge tube 12 and in the stabilization of the plasma torch flame.Compressed air or contaminated air may be injected as a swirl gas 30.The output gas 28 is exhausted through the torch exit 32.

A cross-sectional view of three microwave plasma torches connected inseries 100 is presented in FIG. 2. The apparatus 100 consists of threemicrowave plasma torches 100 a, 100 b and 100 c connected in series.Each microwave plasma torch is connected with cylindrical tubes 54 a and54 b, which are made of brass or stainless steel. The power supplies 24a, 24 b and 24 c, consisted of full-wave voltage double circuit asexplained in FIG. 1, provide the electrical power to the magnetrons 22a, 22 b and 22 c, which generate the microwave radiations and which arecooled by each cooling system 26 a, 26 b and 26 c. The generatedmicrowave radiations are guided through the tapered waveguides 180 a,190 b and 180 c, which deliver effectively the microwave energies intothe discharge tubes 12 a, 12 b and 12 c. The ignition devices 14 a, 14 band 14 c attached to each microwave plasma torch 100 a, 100 b and 100 care fired to initiate plasma generation inside the discharge tubes 12 a,12 b and 12 c. The quartz holders 40 a, 40 b and 40 c made of brass orstainless steel hold the discharge tubes 12 a, 12 b and 12 c. Acylindrical tube 42 a is set up on the bottom of the quartz holder 40 ato transfer contaminated gas stream 16 sucked up by a blower fan 80 intothe plasma torches 10 a, 100 b and 100 c in turn. The blower fan 80 unitmay act like a vacuum cleaner, even swiping surfaces and collectingcontaminants settled on surfaces, if the tube 42 a is made of a flexiblematerial. The flow direction of gas stream 16 is represented by arrows90. The plasma torches are connected in series, so that gas stream 16 tobe purified, after exiting the plasma torch 100 a via the discharge tube12 a, immediately enters the plasma torch 100 b via the quartz holder 40b, after exiting the plasma torch 100 b via the discharge tube 12 b,immediately enters the plasma torch 100 c via the quartz holder 40 c.Each swirl gas, not shown in FIG. 2, is injected through metal pipeline,entering the discharge tubes 12 a, 12 b and 12 c sideways, creatingvortices inside the discharge tubes 12 a, 12 b and 12 c, stabilizing thetorch flames 60 a, 60 b and 60 c. The microwave radiation intensity canbe maximized at the discharge tubes 12 a, 12 b and 12 c by adjusting thedepth of the stubs in the three-stub tuning devices 20 a, 20 b and 20 c.A cylindrical metal tube 42 b is set up on the waveguide 180 c to shieldany leakage of microwaves and to protect the discharge tube 12 c fromany mechanical impact outside. For simplicity, only three microwaveplasma torches are shown in FIG. 2. However, the device 100 can bemodified for efficient decontamination of large volume of air byconnecting more than 3 or less than 3 microwave plasma torches inseries. The number of plasma torches connected in series is determinedby elimination efficiency of the each chemical and biological warfareagents. This number can be determined in terms of the warfare agentspecies, of the each microwave torch power, and of the flow rate ofcontaminated air. The 3 plasma torches in FIG. 2 are determined for thetoluene gas eliminations where 1000 liters per minute of contaminatedair is purified by 1 kW microwave torches. Therefore, this number mustbe modified for each experimental situation.

Experimental results are presented in FIG. 3, which shows the gaschromatography intensity of transmittance of toluene gas. Shown in FIG.3 is the transmittance intensity of the toluene gas measured by a gaschromatography (GC) system for 3 microwave plasma torches connected inseries, as shown in FIG. 2. The GC and the capillary column used in theexperiment have the model numbers of HP 5890 and HP-PLOT Q,respectively, which are manufactured by Hewlet Pakerd (HP) Corporationin U.S.A. The capillary column has 30 m long and 0.53 mm in outerdiameter. The retention time of about 7.5 minute in the horizontal linein FIG. 3 represents signature of the toluene concentration. 850 litersper minute (lpm) of air mixed with toluene gas is used as the input gas16. 70 lpm of compressed air in the plasma torch 100 a, and each 40 lpmof compressed air in the plasma torches 100 b and 100 c are injected asthe swirl gas in this test.Therefore, total flow rate of 1000 lpm entersthe apparatus 100 presented in FIG. 2 of 3 plas torches connected inseries. Length of the connecting tube 54 a and 54 b is optimized to be 7cm for the experimental data in FIG. 3. The toluene concentration was150 particulates per million (ppm). One hundred percent of the toluenecontaminants are transmitted through the discharge tubes withoutelectrical discharges, as presented by the closed square dots in FIG. 3.64.6% of the toluene contaminants are eliminated by three-microwaveplasma torches connected in series when the plasma torches are on, asrepresented by the closed diamond dots in FIG. 3. The most dominantbyproducts after elimination of toluene gas by the microwave plasmatorches are observed to be water (H₂O) and carbon dioxide (CO₂). Theexperiment was carried out five times. Thus, each data point in FIG. 3represents an average value of five data The input microwave power foreach plasma torch is about 1 kW.

A simple first order decay model for treating target chemicals isexpressed as

X/X₀=exp(−E/β),

where X is the concentration of the target chemical agent after themicrowave discharge, X₀ is the initial concentration of the targetchemical agent and E is the energy density joule per liter) of threemicrowave plasma torches connected in series. The factor β representsthe energy density required for bringing down the concentration to 1/eof its initial concentration; i.e. the energy density needed for 63%decomposition. Value of the energy density β for the experimental datapresented in FIG. 3 is 173 joules per liter. This value is much lessthan β=393 joules per liter of the pulsed corona discharge. It is alsoemphasized that a large volume of air can be treated by a compactapparatus in this invention. However, it is pointed out that 1000 lpm ofair passes through the plasma flame of 3 kW for the experimental data inFIG. 3. Therefore, relatively hot air exits from the microwave torch. Infact, the air temperature at 50 cm downstream from the third torch inthe experiment of FIG. 3 is about 80 degree Celsius for the 25 degreeroom temperature. In this context, the air in an isolated room may heatup like a 3 kW electric heater in the room, thereby needing a coolingsystem in summer.

It was observed in the repeated experiments that a synergic effect ofthe plasma torches connected in series is a main reason why thisapparatus works effectively. Experimental data obtained fromexperiments, where 350 lpm air contaminated with 150 ppm toluene gas wastreated by a 1-kW microwave torch, indicated only 35% decomposition oftoluene molecules, which is far less than 64.6% decomposition as shownin FIG. 3. Value of the energy density β is calculated to be 396 joulesper liter for one plasma torch, which is much larger than β=173 joulesper liter in FIG. 3 for 3 torch system. Obviously, the synergic effectof multiple plasma torches connected in series plays a pivotal role inefficient elimination of the chemical and biological warfare agentscontaminated in air. The number of torches connected in series and thelength of the connecting tube 54 a and 54 b are determined by minimumvalue of the energy density β, The experimental data indicates theminimum value of β=173 joules per liter in FIG. 3 for 3 torch systemwith the connecting tube length of 7 cm in eliminating toluene gas by 1kW microwave torches.

A thermo-coupler located about 8 cm away from the bottom of the plasmaflame generated by 1 kW microwave power is about 1800 degree Celsius.The temperature increases drastically to 5500 degree Celsius measured bya spectroscopy, as the observation point approaches the bottom center ofthe flame. Most of the microwave power is used for ohmic heating of theflame center at a very high temperature. But, this plasma flame elementdrifs away from the center due to air blow, cooling its temperature asthe fluid element of air moves away from the center. Temperature of anyphysical object like microbes moving with the plasma flame element istherefore very high due to the radiation emitted from the flame centerand due to the gas temperature of the flame. The airborne biologicalwarfare agents mixed in air can be eliminated by the high temperature ofthe plasma torch flames. The biological warfare agents are finelyaerosolized to be airborne. For example, anthrax spores are attached onfine organic or inorganic particles with submicron size, floating freelyin air.

In order to simulate killing of the biological warfare agents,vitrification experiments of sewage sludge powders are carried out.Sewage sludge powders used in the experiment were pulverized in thediameter of about 50˜500 micrometer and dried up to the moistureconcentration of 10%. This experiment was done using only one microwaveplasma torch of 1 kW power. The powders were injected through thedischarge tube with air as a carrier gas. The powder beforevitrification is very fine as prepared. The microscopic picture of 50magnifications of the leftover ashes after vitrification experimentshows glassified grains, which are significantly larger than the initialsize of the powder. Obviously, the powders were vitrified by hot localtemperature of the microwave plasma torch. Volume of the sludge powersreduces considerably after passing through the microwave plasma torch,indicating that most of the hydrocarbons in the sludge were burnt out.The vitrification experiment of the sludge powers clearly indicates thatthe airborne biological warfare agents like microbes or bacteriaattached on organic or inorganic aerosols may bum and die, as they passthrough a microwave plasma torch, vitrifying the leftover ashes fromburnout. Efficiency of the aerosol elimination was measured by makinguse of airborne soot emitted from a diesel engine. Remember thatbiological warfare agents are attached on the aerosol particles. Thus,elimination of aerosol in air is an effective means of killing ofbiological warfare agents. An intentionally-spoiled diesel engineproduces a fair amount of soot, which are fine particulates made ofcarbon molecules. The soot elimination is measured by a collection ofthe soot on a white filter. The experimental data indicate thatsignificantly more than 90% of the soot emitted from a 2000 cc dieselengine, operating with 2000 rpm, is eliminated by 3 plasma torchesconnected in series for the physical parameters identical to theexperiment for FIG. 3. Flow rate of the discharge gas from the dieselengine used in this experiment is 4000 lpm, although the gas temperatureis high. This experiment indicates that the aerosols in a large flowrate may effectively eliminated by the present invention. Thisexperiment also clearly demonstrated that soot from the diesel enginesin buses, trucks and ships can be eliminated by the apparatus of thepresent invention. For optimum result, the discharge gas can be recycledthrough the system. If there are any harmful residues, ashes, byproductsare still remain in the discharge gas, the conventional system such asscrubbers, absorbers, etc, can be attached to the present invention forelimination of these leftovers.

Although this embodiment is the apparatus for elimination of airbornetoluene gas and airborne sludge powders, the invention is not limited tothe use of the elimination of toluene gas and sludge powders. Withoutdeparting from the spirit of the invention, numerous otherrearrangements, modifications and variations of the present inventionare possible in light of the foregoing teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described.

What is claimed is:
 1. An apparatus for eliminating chemical andbiological warfare agents in air, said apparatus comprising: (a)microwave plasma torches connected in series for optimum synergiceffects, wherein each microwave plasma torch includes an input tube forinjection of air contaminated with said agents into said microwaveplasma torch and an output tube for discharging the treated gas streamfrom said microwave plasma torch; (b) the first microwave plasma torchand the second microwave plasma torch connected in series, wherein theinput tube of the second microwave plasma torch is aligned fortransferring the gas stream discharged from the output tube of the firstmicrowave plasma torch; (c) several microwave plasma torches connectedin series, wherein said microwave plasma torches are aligned in the samedirection as the gas stream; (d) individual power supply for each of thesaid microwave plasma torches, wherein each of said microwave plasmatorches forms a plasma flame such that gaseous or biological species aredestroyed and burn out; and (e) individual ignition device for each ofsaid microwave plasma torches.
 2. In the apparatus according to claim 1,wherein a suction fan is attached to the first microwave plasma torch toinject air contaminated with said agents, and wherein the suction fanunit functions as a vacuum cleaner collecting contaminants settled onsurfaces to be decontaminated.
 3. A multi-step process for optimumsynergistically eliminating chemical and biological warfare agents inair by passing said air contaminated with said agents through aplurality of serially connected microwave plasma torches wherein eachmicrowave plasma torch consists of an input tube for introduction ofsaid contaminated air, a plasma formation zone and an output tube fordischarging the treated gas, said process comprising: (a) initiallypassing at least 1000 liters per minute of said contaminated air throughthe input tube of the first microwave plasma torch unit operating at2.45 GHz and 0.6-1.4 kW power range; (b) sending the decontaminated gasfrom said first plasma unit into a second plasma unit; (c) repeatingsteps (a) and (b) through a plurality of serially-connected, plasmaunits to accomplish a desired level of decontamination.
 4. In theprocess according to claim 3, wherein the contaminated air as a swirlgas is injected into said plasma formation zone to stabilize the plasma,forming a vortex flow for each microwave plasma torch.
 5. The processaccording to claim 4, wherein the contaminated air stream and additionalmakeup air mix in said plasma formation zone.